PHY213_Chapter28_Sec1to4

PHY213_Chapter28_Sec1to4 - Chapter 28 Atomic Physics Atom...

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Chapter 28 Atomic Physics
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General Physics Atom Physics Sections 1–4
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General Physics Importance of Hydrogen Atom Hydrogen is the simplest atom Enables us to understand the periodic table Ideal system for performing precise comparisons of theory with experiment Much of what we know about the hydrogen atom can be extended to other single-electron ions For example, He + and Li 2+
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General Physics Sir Joseph John Thomson “J. J.” Thomson 1856 - 1940 Developed model of the atom Discovered the electron Did extensive work with cathode ray deflections 1906 Nobel Prize for discovery of electron
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General Physics Early Models of the Atom Newton’s model of the atom was a tiny, hard, indestructible sphere J.J. Thomson’s model of the atom A volume of positive charge Electrons embedded throughout the volume
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General Physics Rutherford’s Scattering Experiments The source was a naturally radioactive material that produced alpha particles (He ++ ) Most of the alpha particles passed though the gold foil A few deflected from their original paths Some even reversed their direction of travel Active Figure: Rutherford Scattering
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General Physics Rutherford Model of the Atom Rutherford, 1911 Planetary model Based on results of thin foil experiments Positive charge is concentrated in the center of the atom, called the nucleus Electrons orbit the nucleus like planets orbit the sun
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General Physics Rutherford Model, Problems Atoms emit certain DISCRETE characteristic frequencies of electromagnetic radiation The Rutherford model is unable to explain this phenomena Rutherford’s electrons are undergoing a centripetal acceleration and so should radiate electromagnetic waves at a frequency related to their orbital speed The radius should steadily decrease and the speed should steadily increase as this radiation is given off The electron should eventually spiral into the nucleus, but it doesn’t The radiation frequency should steadily increase – should observe a continuous spectrum of radiation at progressively shorter and shorter wavelengths, but you don’t
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General Physics Emission Spectra When a high voltage is applied to a gas at low pressure, it emits light characteristic of the gas When the emitted light is analyzed with a spectrometer, a series of discrete bright lines is observed - emission spectrum Each line has a different wavelength and color
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General Physics Emission Spectrum of Hydrogen – Equation The wavelengths of hydrogen’s spectral lines experimentally agree with the equation R H is the Rydberg constant R H = 1.0973732 x 10 7 m -1 n is an integer, n = 3, 4, 5, 6, … The spectral lines correspond to different values of n = λ 2 2 H n 1 2 1 R 1
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General Physics Spectral Lines of Hydrogen The Balmer Series has lines whose wavelengths are given by the preceding equation Examples of spectral lines n = 3, λ = 656.3 nm n = 4, λ = 486.1 nm n = 5, λ = 434.1 nm n = 6, λ = 410.2 nm
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This note was uploaded on 08/25/2009 for the course PHY 213 taught by Professor Cao during the Summer '08 term at Kentucky.

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PHY213_Chapter28_Sec1to4 - Chapter 28 Atomic Physics Atom...

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